Physical and chemical interaction mechanisms in silicone rubbers^†

Silicone rubbers were prepared with graded concentrations of two different fillers—conventional silica capable of both physical and chemical interactions with the methyl vinyl siloxane polymer and magnetic ferrite powder capable of physical interaction only. The mechanical properties of the experimental rubbers (containing both these fillers at the same time) gave characteristic plots of property isolines in the two filler concentration coordinates. To obtain theoretical counterparts of these plots, physical considerations were used to define the polymer–filler contact surface area in real polymer–filler systems and to derive probable variants of its filler concentration dependence. A mathematical model of the polymer–filler interaction was developed and was explored by computing a series of model diagrams. Comparison of the experimental and computed plots indicated that, even with a chemically active filler present, physical interaction mechanisms are dominant; their contribution in determining the mechanical properties of filled silicone rubbers appears to exceed 93%.